I believe this is correct. Fear of a snake isn't irrational because it resides in a very primitive part of our brain. But when that fear becomes prohibitive and makes it difficult for you to do every-day things then it has become irrational. That's where exposure therapy can be successful. Its not going to eliminate that primitive fear. That's almost instinct in humans at this point. But it is going to make it so you can watch TV without worrying about seeing a snake on it. Or, rather, make it so you don't care that there's a snake on it I guess.